In part to explore the specific signaling pathways that underlie the co-dependency between muscle and bone, we have developed a novel in vivo murine model of transient muscle paralysis that inhibits both motor and sensory signaling following intramuscular injections of botulinum toxin A (BTxA). Despite a mild and transient gait deficit, we have shown that the loss of trabecular bone following transient muscle paralysis is rapid and profound and dominated by RANKL mediated osteoclastic resorption. Our preliminary data with a mouse hindlimb specific defect in proprioception has led us to hypothesize that trabecular bone homeostasis is modulated by neuromuscular proprioception. In this project we will pursue this thesis through four closely related sub-hypotheses each with a corresponding Specific Aim. The first three S. Aims seek to demonstrate that while mechanical stimuli clearly influence trabecular bone homeostasis, muscle proprioception plays a previously unrecognized, but fundamental role in modulating local trabecular bone morphology. In the final S. Aim we will attempt to clarify that a neuronally mediated inflammatory response precedes and mediates the profound osteoclastic resorption acutely induced by transient muscle paralysis. If these data support our hypothesis, we believe that our results hold potential to alter current approaches to intervene or prevent bone loss in a variety of musculoskeletal pathologies. PUBLIC HEALTH RELEVANCE: This project seeks to elucidate a fundamental, but as yet unrecognized neuronal pathway by which normal trabecular bone homeostasis is achieved and maintained. From a clinical perspective, we believe that understanding the role that sensory proprioception plays in modulating local trabecular bone homeostasis will directly enable novel interventions into both acute (e.g., spinal cord injury, general disuse) and chronic (e.g., associated with aging) bone loss pathologies.